Thermosensitive relay



Jan. 11,1944. G. L. PEARSON 2,339,029

- THERMOSENSITIVE RELAY Filed Sept. 24, 1941 M/ VE/V TOR a. L PEARSON WWW-ma:

A T TO/QA/EV Patented llan. 11, 1944 THERMOSENSITIVE RELAY Gerald L. Pearson, Mlllington, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation or New York I Application September 24, 1941, Serial No. 412,068

12 Claims.

This invention relates to electrical resistors having pronounced temperature coeflicients of resistance'and particularly to the use of these resistors for circuit controlling purposes.

An object of the invention is to provide an improved thermosensitive resistor that functions as a relay to operate a responsive circuit.

Another object is to provide an improved resistor for producing a time delay in the operation of an electric circuit.

It is well known that electric circuits may be operatively controlled through the use of directly heated resistors having a high negative temperature coefiicient of resistance, wherein the resistor exhibits a high resistance at low temperatures and a lowresistance at high temperatures. A resistorof this type usually comprises a heater conductor embedded within a mlnute'bead. oi semiconductive substance having a high negative temperature coeflicient of resistance, the two ends of the conductor being generally connected tov an energizing circuit. The resistor of this type also includes two ends of a pair of conductors terminated in the semiconductive substance, the other ends thereof being connected to a responsive circuit. Upon energization of the heater circuit. current flows through the heater conductor, and the heat generated therebyv raises the temperature of the bead whereby the resistance thereof drops appreciablyo This reduction of resistance in the bead consequently lowersv the resistance of the responsive circuit and causes energization thereof, inasmuch as the material of the bead is in series with the ends of the conductors terminated therein. Control of the responsive circuit is the heater conductor on the semiconductive material of the bead. This control, however, is limited because of the comparatively low impedance characteristic of the heater conductor and as a result necessitates substantial current drain in order to obtain the required heating efiect.

In accordance with this invention, a novel directly heated resistor, comprising a bead of high negative temperature coeificient of resistance, is utilized as a relay for controlling the operation of an electric circuit, wherein the semiconductive material itself replaces the heater conductor as the heating element. By employing the comparatively high impedance semiconductive material, rather than a continuous conductor, 'as a heating element applicant has provided a more flexible and economical means for controlling subsidiary circuits, since a smaller therefore obtained through the heating efiect of P value of current can be applied. Use of the semiconductive material as a heating means is obtained by terminating the heater circuit conductors individually therein, so that the semiconductive material is serially connected with the heater conductors.

In arrangements where more than one pair of conductors has been terminated in a semiconductive substance, it has been heretofore difficult to direct current flow through the proper channels. As far as applicant is aware, resistors of high negative temperature coefiicient having more than two conductors embedded within a semiconductive substance are limited to the type wherein the heating element comprises a continuous conductor embedded within the material. Applicant has overcome this limitation, in one embodiment, by spacing four conductors conjugately with respect to each other. The con- Jugate relationship existing among the conouctors, disregarding thermal effects, is such that a change in the impressed electromotive force in one circuit does not produce a change in the current of another circuit. This is based on the well-known theory that equipotential planes of varying magnitude exist between two conductors of a circuit. In this instance, assume an imaginary line between the two heater conductors terminated in the semi-conductive substance. Equipotential planes of varying magnitude exist along this line and at right angles thereto. As the two conductors of the responsive circuit are conjugately placed with respect to the heater conductors they are therefore positioned along one of the equipotential planes. I

Consequently, there is no potential 'difierence between the responsive circuit conductors and as a result current is not induced in the responsive circuit by flow of current in the heater circuit. Furthermore, the heater current continues through the semiconductive material between the heater conductor terminations rather than circuitously through the responsive circuit.

In another embodiment applicant has paired the quadruplex conductors and has terminated each pair in an individual bead of semiconductive material having a high negative temperature coeflicient of resistance. Both beads are then embedded in a thermal medium such as glass. Current flow through the proper circuit is thereby assured and the delaying action of one circuit upon another may also be increased.

A feature of this invention therefore resides in a. high negative temperature coeflicient resistor having a pair of actWatingcircuit conductors and a pair of responsive circuit conductors terminated conjugately in a head of semi-conductive material.

Another feature resides in a high negative temperature coemcient resistor having a pair of heater circuit conductors and a pair of responsive cirobtained from a consideration of the followin detailed description read in connection with the accompanying drawing in which:

Fig. 1 illustrates one embodiment of the invention in which a resistorbead having a high neg.- ative temperature coefilcient of resistance has terminated therein four conductors spaced at conjugate points;

Fig. 2 illustrates a sectional view of the resistor taken along line 2-2 of Fig. 1;

Fig. 3 illustrates a circuit application of Fig. 1 as a delaying device;

Fig. 4 illustrates another. embodiment of the invention in which a pair of resistor beads, each having a pair of conductors'terminated therein, are interconnected by a thermal medium; and

Fig. 5 illustrates a' circuit application of Fig. 4 as a delaying device.

High negative temperature coefilcient resistors exemplified as time delay relays herein may be made from combinations of metal oxides as taught in the application of Richard O. Grisdale,

Serial No. 274,ll4,-flled May 1'7, 1939, now-Patent 2,258,646, issued October 14, 1941. By the employment of proper proportions of the oxide for the resistance material, series of units may be made having a wide range of specific resistance but always in a comparatively narrow range of high resistance temperature coefficient. It has been .found that mixtures of nickel and manganese oxides when properly heat treated combine to produce a resistance material having particularly desirable resistance characteristics.

Referring to the drawing and particularly to Figs. 1 and 2, a resistor bead I comprises a selected semiconductive material H such as disclosed, for example, in the aforementioned Grisdale application, which material has a high resistance to current flow at ordinary room temperatures while a low resistance to current how at high temperatures. Within the material II are terminated conducting leads I2, l3 and l4,

IS in conjugate relationship therewith. ,By placing the conductors l2, l3, and It, It conjugately, current flow is directed through the desired circuit; for example, if we consider conductors l2, l3 connected to a primary circuit and conductors l4, l connected to a secondary circuit, an electromotive force impressed across conductors l2, I3 will cause current to flow from conductor l2 serially through the semiconductive material and thence to conductor 13 without passing duced in the circuit comprising conductors l4, II.

An embodiment of this invention as a time retardation relay is exemplified in Fig. 3, which discloses a responsive circuit R activated through a four-terminal thermal resistor relay III, of the above-described design, by a heating circuit H. The activating or heating circuit H contains a high voltage battery ll, current limiting resistance l8, and key l9 connected serially through the semiconductive material ii to two opposite conductors l2, l3 of the thermal resistor relay [0. The responsive circuit R comprises a low voltage battery 2| and an electroresponsive relay 22 connected in series to the other two conductors l4, IS. The battery voltage 2| is lower than the maximum voltage of the thermal relay 'lll characteristic so that under normal conditions only a small current flows in this circuit. This the heater current flow through the semiconductive material ll raises the temperature and in turn lowers the resistance thereof. It is to be noted that the main heating element herein comprises the semiconductve material itself and not the conductors l2, l3. When the maximum voltage of relay II] is less than the voltage of battery 2 I, the responsive circuit R becomes unstable and current in the responsive circuit R increases to a value which is more than sufficient to operate relay 22. The operation of relay 22 closes the lower front contact springs thereof and initiates a circuit operation, which forms no part of the invention and which'is therefore not shown in the drawing. When the key I9 is again opened, current cntinues to flow, however, in the responsive circuit R until its circuit is opened. Circuit opening means for the responsive circuit R is not shown as it also forms no part of the invention.

It is advantageous in some applications to have one circuit in a four-terminal thermal resistor insulated electrically from the other circuit while at the same time both circuits are coupled thermally. This type of unit may be constructed by sealing two spaced beads of semi-conductive substance having a high negative temperature coefiicient of resistance in a glass rod or other suitable thermal means. Each bead also includes a pair of conductors terminated therein for connection to the external circuit.

As shown in Fig. 4, resistor 25 comprises a pair of spaced high negative temperature coemcient ofresistance beads 26, 21 disposed within a glass rod 28 or other suitable thermal means. The separation of the beads 26, 21 is determined by the time delay desired, the retardation effect being greater the, further apart the beads are placed. Each b'ead comprises a pair of conductors embedded therein, bead 26 including conductors 29, 30 and bead 21, conductors 3|, 32.

Fig. 5 illustrates an application of the resister 25 to an electric circuit arrangement similar to that described in Fig. 3. In this arrangement when key 33 is closed, current is provided for heating resistor bead. 26 in a circuit traced from key 33, through current limiting resistance 34, battery 35, conductor 30, across semiconductive substance 26 to conductor 29, and thence back to key 33. The initial current, which is determined by the cold resistance of the bead 26, is small and rises slowly at first, then more rapidly as the bead becomes hot. The final current, which continues to flow until the circuit is opened, is limited by the resistance 34. The heat from bead 26 is transferred along the glass rod 28 to head 21, which after a predetermined time interval heats sufficiently to lower its impedance to a value which causes suflicient current flow to energize relay 3G in an obvious circuit. Key 33 may be opened upon energization of relay 36, which continues energized until opened externally (not shown).

While this invention has been shown and described as embodying certain features, merely for the purpose of illustration, it will be understood that it can be used in many other widely varying fields without departing from the spirit of the invention and scope of the appended, claims.

- What is claimed is:

1. A resistor comprising semiconductive substance having ,a pronounced temperature coeflicient of resistance, and two pairs of conductors having individually spaced ends thereof terminated within said substance, said pairs of conductors being so disposed that energization of one of said pairs renders said substance conductive to effect a low resistance path in the other pair of conductors.

2. In a resistor, a unit comprising a semiconductive material having a high negative temperature coefiicient of resistance, and four conductors having individually spaced. ends thereof so disposed within said unit that said material is circuitously connected with said conductors, one pair of said conductors adaptable for connection to an energizing circuit for heating said material, the other pair adaptable for connection to a responsive circuit, characterized by this that upon energization of the first pair said material increases in temperature and correspondingly decreases in resistance until said material is rendered conductive to effect a low resistance path in the other pair of conductors thereby energizing the responsive circuit.

3. A resistor comprising electrical semiconductive material having a negative temperature coefficient of resistance, and fourconductors terminated within said material, said conductors being terminated at conjugate points.

4. A resistor unit comprising a bead of semiconductive material having a high negative temperature coeflicient of resistance, and four conductors having ends thereof embedded and terminated within said bead, said conductors be spaced symmetrically and being terminated conjugate points.

5. A resistor unit. comprising an electrical insulating, heat conducting medium, a plurality of beads of semiconductive material having a high temperature coefiicient of resistance included within said medium, and a plurality of conductors terminated in each of said beads.

6. A directly heated resistor unit comprising a pair of beads of semiconductive material having a high negative temperature coefiicient of resistance, a glass medium in which said beads are embedded in spaced relationship, and a pair of conductors terminated in each of said beads, whereby said pairs of conductors are electrically insulated and thermally coupled.

'7. A circuit controlling device comprising two .pairs of conductors connected respectively to a primary and secondary circuit, an electrical semi- I conductive substancehaving a high temperature coefiicient of resistance, said pairs of conductors having ends thereof individually embedded in the substance and spaced to introduce a time element in the influence of the primary circuit over the secondary circuit, means in said primary circuit for rendering said substance conductive, and means in said secondary circuit responsive to the conductivity of said substance.

8. A resistor comprising four conductors connected respectively to the two terminals of a primary and secondary circuit, a semiconductive material having a'high negative temperature coefficient of resistance, said conductors having 1 ends thereof individually terminated within said material at conjugate points, means in said primary circuit for rendering saidmaterial conductive, and means in said secondary circuit responsive to the conductivity of said material.

9. A directly heated resistor comprising semiconductive material having a high resistance temperature coeflicient, a plurality of spaced conductors having ends thereof individually terminated within said material, said conductors being grouped into pairs and spaced so that the resistance between the conductors of each pair is less than that between the conductors of separated pairs, a normally open primary circuit connected in series with one pair of said conductors, a normally closed secondary circuit connected in series with another pair of said conductors, a source of energy in said secondary circuit normally insufficient to cause efiective current flow through said material, and a source of energy in said primary circuit to render said material conductive, whereby the energy of said secondary circuit is rendered effective.

10. In combination, a primary circuit and a secondary circuit, a device coupling said primary circuit to said secondary circuit, said device comprising electrical semiconductive material having a high temperature coeflicient of resistance, a pair of spaced electrical conductors having ends thereof embedded in said material and connected to said primary circuit, a second pair of spaced electrical conductors embedded in said material and connected to said secondary circuit, the resistance between the conductors of each pair being less than that between the conductors of separated pairs, a source of potential in said secondary circuit, said potential being insuflicient normally to circulate eifective current through said secondary circuit because of the normally high resistance of said semiconductive material, and a source of energy in said primary circuit to render the material conductive, whereby the potential of said secondary circuit is rendered effective to cause current flow therein.

11. A circuit controlling device comprising a pair of beads of electrical semiconductive substance having a high negative temperature coefilcient of resistance, a pair of spaced conductors individually terminated'within each of said beads, a glass rod enclosing said beads in spaced relationship with said conductors extending through the glass rod, a heating circuit con nected to one pair of said conductors, a responsive circuit connected to another pair of the conductors, means in said heating circuit for raising the temperature of said substance 'to render same conductive, and means in said responsive circuit energized lay-reason oi the conductivity of said substance.

12. A resistance bead comprising semiconductive material having a high negative tem- Jerature coefficient of resistance, a pair of coni ductors having spaced ends thereof terminated by aquipotential planes of varying magnitude are produced in the material between said terminated conductors, and a second pair of conductors having ends thereof terminated within said material, said second pair of conductor ends being terminated along one of said equipotential planes.

GERALD L. PEARSON; 

